Pliers-type hand tools with toggle-locking mechanisms are generally known as toggle wrenches or locking pliers. These tools usually comprise a fixed handle with a fixed jaw on one end and a movable jaw with a movable handle. The jaws may be shaped to function as long nose pliers, ordinary wrenches with curved serrated jaws, jaws in the shape of C-clamps, C-clamps with swivel pads, hole punches, or any other kind of hand tool where the toggle-locking action is useful.
These hand tools are so constructed that once the movable jaw is adjusted to seize a workpiece firmly between the movable and the fixed jaw and then the handles are tightly compressed, the toggle mechanism locks the hand tool onto the workpiece. Thereafter the hand may be withdrawn, yet the tool will remain firmly locked in place. This clamping action often requires much force. Frequently, the tool is misadjusted when being clamped, so that it is extremely difficult to release the locked tool. Sometimes it takes as much applied force to open a toggle-locking hand tool as to clamp it onto the workpiece. Tool adjustments are generally made by turning an adjusting screw engaging the fixed handle and modifying physical dimensions in the toggle mechanism.
Oftentimes, a locking hand tool is used in such a confined work space that once it is locked on the workpiece in a compressive motion, there is not enough room for two hands to force it open. Also forcing open a locking hand tool may result in a springing action, which may take the worker unaware, and can cause abrasion or mild injuries to the hands by pushing the hands against adjacent objects. For all these reasons, it is useful to install quick release mechanisms on locking hand tools of the toggle type.
In a conventional locking hand tool, there are three pivot points in what is known as the "power line" from the pivot point of the movable handle on the movable jaw down through an inner pivot near the end of the spanning toggle link. The other end of the toggle link rests pivotably at the tip of the adjusting screw in the channel of the fixed handle. Locking the handle causes the center pivot point to cross the "power line" between the two outer pivots. Unlocking the conventional locking hand tool involves forcing the single center pivot back across the "power line". Usually, this is carried out by means of a release lever pivotably mounted in the channel of the movable handle. The release lever is pushed against a projection on the toggle link, thus causing the toggle link to pivot outward and drive the two handles apart to release the clamping action of the jaws.